General Concepts

Redux is all about functional programming and pure functions. Understanding these concepts is crucial to understanding the underlying principles of Redux.

Functional programming centers around avoiding changing state and mutable data—in other words, making your code predictable and free of side effects.

JavaScript allows you to write code in a functional style, as it treats functions as first-class objectsYou can store functions in variables, pass them as arguments to other functions, and return them as values of other functions.. However, JavaScript was not designed to be a functional programming language, so there are some caveats that you will need to keep in mind.

Pure and impure functions

A pure function returns values by using only its arguments: it uses no additional data, changes no data structures, touches no storage, and emits no external events (like network calls). This means that you can be completely sure that you will always get the same result every time you call the function with the same arguments. Here is an example of pure functions: